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Date:   Tue, 5 May 2020 07:55:00 +0200
From:   Michał Orzeł <michalorzel.eng@...il.com>
To:     Sean Paul <seanpaul@...omium.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Dave Airlie <airlied@...ux.ie>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] drm: Replace drm_modeset_lock/unlock_all with
 DRM_MODESET_LOCK_ALL_* helpers



On 04.05.2020 13:53, Daniel Vetter wrote:
> On Fri, May 01, 2020 at 05:49:33PM +0200, Michał Orzeł wrote:
>>
>>
>> On 30.04.2020 20:30, Daniel Vetter wrote:
>>> On Thu, Apr 30, 2020 at 5:38 PM Sean Paul <seanpaul@...omium.org> wrote:
>>>>
>>>> On Wed, Apr 29, 2020 at 4:57 AM Jani Nikula <jani.nikula@...ux.intel.com> wrote:
>>>>>
>>>>> On Tue, 28 Apr 2020, Michal Orzel <michalorzel.eng@...il.com> wrote:
>>>>>> As suggested by the TODO list for the kernel DRM subsystem, replace
>>>>>> the deprecated functions that take/drop modeset locks with new helpers.
>>>>>>
>>>>>> Signed-off-by: Michal Orzel <michalorzel.eng@...il.com>
>>>>>> ---
>>>>>>  drivers/gpu/drm/drm_mode_object.c | 10 ++++++----
>>>>>>  1 file changed, 6 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/drm_mode_object.c b/drivers/gpu/drm/drm_mode_object.c
>>>>>> index 35c2719..901b078 100644
>>>>>> --- a/drivers/gpu/drm/drm_mode_object.c
>>>>>> +++ b/drivers/gpu/drm/drm_mode_object.c
>>>>>> @@ -402,12 +402,13 @@ int drm_mode_obj_get_properties_ioctl(struct drm_device *dev, void *data,
>>>>>>  {
>>>>>>       struct drm_mode_obj_get_properties *arg = data;
>>>>>>       struct drm_mode_object *obj;
>>>>>> +     struct drm_modeset_acquire_ctx ctx;
>>>>>>       int ret = 0;
>>>>>>
>>>>>>       if (!drm_core_check_feature(dev, DRIVER_MODESET))
>>>>>>               return -EOPNOTSUPP;
>>>>>>
>>>>>> -     drm_modeset_lock_all(dev);
>>>>>> +     DRM_MODESET_LOCK_ALL_BEGIN(dev, ctx, 0, ret);
>>>>>
>>>>> I cry a little every time I look at the DRM_MODESET_LOCK_ALL_BEGIN and
>>>>> DRM_MODESET_LOCK_ALL_END macros. :(
>>>>>
>>>>> Currently only six users... but there are ~60 calls to
>>>>> drm_modeset_lock_all{,_ctx} that I presume are to be replaced. I wonder
>>>>> if this will come back and haunt us.
>>>>>
>>>>
>>>> What's the alternative? Seems like the options without the macros is
>>>> to use incorrect scope or have a bunch of retry/backoff cargo-cult
>>>> everywhere (and hope the copy source is done correctly).
>>>
>>> Yeah Sean & me had a bunch of bikesheds and this is the least worst
>>> option we could come up with. You can't make it a function because of
>>> the control flow. You don't want to open code this because it's tricky
>>> to get right, if all you want is to just grab all locks. But it is
>>> magic hidden behind a macro, which occasionally ends up hurting.
>>> -Daniel
>> So what are we doing with this problem? Should we replace at once approx. 60 calls?
> 
> I'm confused by your question - dradual conversion is entirely orthogonal
> to what exactly we're converting too. All I added here is that we've
> discussed this at length, and the macro is the best thing we've come up
> with. I still think it's the best compromise.
> 
> Flag-day conversion for over 60 calls doesn't work, no matter what.
> -Daniel
> 
I agree with that. All I wanted to ask was whether I should add something additional to this patch or not.

Thanks,
Michal
>>
>> Michal
>>>
>>>> Sean
>>>>
>>>>> BR,
>>>>> Jani.
>>>>>
>>>>>
>>>>>>
>>>>>>       obj = drm_mode_object_find(dev, file_priv, arg->obj_id, arg->obj_type);
>>>>>>       if (!obj) {
>>>>>> @@ -427,7 +428,7 @@ int drm_mode_obj_get_properties_ioctl(struct drm_device *dev, void *data,
>>>>>>  out_unref:
>>>>>>       drm_mode_object_put(obj);
>>>>>>  out:
>>>>>> -     drm_modeset_unlock_all(dev);
>>>>>> +     DRM_MODESET_LOCK_ALL_END(ctx, ret);
>>>>>>       return ret;
>>>>>>  }
>>>>>>
>>>>>> @@ -449,12 +450,13 @@ static int set_property_legacy(struct drm_mode_object *obj,
>>>>>>  {
>>>>>>       struct drm_device *dev = prop->dev;
>>>>>>       struct drm_mode_object *ref;
>>>>>> +     struct drm_modeset_acquire_ctx ctx;
>>>>>>       int ret = -EINVAL;
>>>>>>
>>>>>>       if (!drm_property_change_valid_get(prop, prop_value, &ref))
>>>>>>               return -EINVAL;
>>>>>>
>>>>>> -     drm_modeset_lock_all(dev);
>>>>>> +     DRM_MODESET_LOCK_ALL_BEGIN(dev, ctx, 0, ret);
>>>>>>       switch (obj->type) {
>>>>>>       case DRM_MODE_OBJECT_CONNECTOR:
>>>>>>               ret = drm_connector_set_obj_prop(obj, prop, prop_value);
>>>>>> @@ -468,7 +470,7 @@ static int set_property_legacy(struct drm_mode_object *obj,
>>>>>>               break;
>>>>>>       }
>>>>>>       drm_property_change_valid_put(prop, ref);
>>>>>> -     drm_modeset_unlock_all(dev);
>>>>>> +     DRM_MODESET_LOCK_ALL_END(ctx, ret);
>>>>>>
>>>>>>       return ret;
>>>>>>  }
>>>>>
>>>>> --
>>>>> Jani Nikula, Intel Open Source Graphics Center
>>>
>>>
>>>
> 

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